Diodes are well known electronic components that tend to conduct electric current in only one direction. A diode includes a p-type region (e.g, a semiconductor region doped with a p-type material) and an n-type region (e.g., a semiconductor region doped with n-type material). The p-type region and the n-type region may be coupled together at a junction to form a PN junction diode or separated by an intrinsic (i) type region to form a PIN diode. The diode further includes two metal contacts (i.e., electrodes) called the anode and the cathode that are coupled to the p-type region and the n-type region, respectively. When the anode is positively charged relative to the cathode at a voltage greater than a certain minimum voltage, i.e., the turn-on voltage, current flows through the diode from the p-type region to the n-type region. Diodes having metal contacts that terminate on the same plane (i.e., coplanar) are planar diodes.
FIG. 1A depicts a partial plan view of a prior art planar PIN diode 100 and FIG. 1B is a cross-sectional view of the planar diode 100 of FIG. 1A, with like elements having identical numbers. For descriptive purposes, the partial plan view depicted in FIG. 1A excludes certain layers depicted in FIG. 1B, such as silicon dioxide layers 114, silicon nitride layers 116, and a glass layer 118. Additionally, the partial plan view depicts only the portions of metal contacts 110 and 112 that are in contact with underlying semiconductor regions 104 and 106.
The planar diode 100 is fabricated on a semiconductor wafer 102 by creating a p-type region 104 and an n-type region 106 that are separated by an i-type region 108. As shown in FIGS. 1A and 1B, the n-type region 106 surrounds the i-type region 108 and the p-type region 104. The i-type region 108 is a planar region beneath and larger than the p-type region 104 and the n-type region 106 is a planar region beneath and larger than the i-type region 108.
Electrical contact with the p-type region 104 is facilitated by the addition of a metal contact 110 on top of and coupled to the p-type region 104. Likewise, electrical contact with the n-type region 106 is facilitated by the addition of a metal contact 112 coupled to the n-type region 106. As illustrated, the metal contacts 110, 112 are separate, distinct circular regions.
Silicon dioxide layers 114 and silicon nitride layers 116 reduce parasitic capacitance and provide an interface between the wafer 102 and a glass layer 118. The glass layer 118 further reduces parasitic capacitance and acts as a low-loss substrate for transmission lines. The metal contacts 110 and 112 are coupled to the p-type region 104 and the n-type region 106, respectively, through contact holes 120 and 122 that extend through the silicon dioxide layers 114, silicon nitride layers 116, and glass layer 118.
Diodes are used in many electronic applications. To select a diode for use in a particular application, the characteristics of the diode are matched to the particular application. One common diode characteristic is switching speed, which is a measure of how quickly the diode turns off (i.e., achieves a high impedance state) when switched from forward conduction to reverse conduction. There is an ever present need for diodes with improved switching speeds. The present invention fulfills this need among others.